Observations of the interstellar comet 3I/ATLAS by spacecraft on Mars are helping scientists learn more about how to protect our planet from dangerous space rocks.
Comet 3I/ATLAS originated about 7 billion years ago around a star system elsewhere in the Galaxy.
More on 3I/ATLAS
It's temporarily passing through our cosmic environs.
3I/ATLAS poses no threat to Earth, but planetary defence experts have been studying it with a view to learn more about refining the trajectory of such objects, as part of an overall plan to keep Earth safe.
A view behind the Sun
Comet 3I/ATLAS is the third interstellar object ever observed, and was discovered on 1 July 2025.
Since its discovery, scientists have been using ground-based and space-based telescopes to learn more about where it came from, and where it's headed.
In early October 2025, 3I/ATLAS disappeared behind the Sun, from our perspective on Earth.
Cunningly, scientists were able to call on spacecraft at Mars to keep track of the comet, while it wasn't visible to us.
Between 1 and 7 October 2025, the European Space Agency's Mars Express and ExoMars Trace Gas Orbiter spacecraft observed comet 3I/ATLAS as it passed close to the Red Planet.
Those observations, say the European Space Agency, have improved the comet’s predicted location by a factor of 10.
"By being able to use Mars-based data for an unusual observation, we learned more about the interstellar comet’s path through our Solar System in a valuable test case for planetary defence, even though 3I/ATLAS does not pose any danger," a statement from ESA said.
The Trace Gas Orbiter got views 10 times closer to 3I/ATLAS than telescopes on Earth, and also managed to see it from a different angle.
Triangulating that data gathered on Mars with the previous data gathered from Earth has helped scientists predict the comet's path much more accurately.
How comet 3I/ATLAS is helping protect our planet
3I/ATLAS is passing through our Solar System at speeds of up to 150,000 mph (250,000 kph) and will soon leave it forever.
Improving the known trajectory of this comet is a big deal, since it's only the third such object we've ever seen.
The planetary defence team at ESA’s Near-Earth Object Coordination Centre had to account for the fact that the comet was being observed by a spacecraft on Mars, not a telescope on Earth.
Normally, observations are made from observatories on Earth, and sometimes a space telescope orbiting Earth.
But this time, the observations were made by a spacecraft orbiting Mars at speed.
They had to work with several teams across the European Space Agency to calculate exactly where the Trace Gas Orbiter was when it made its observations of 3I/ATLAS.
The data gathered marks the first time such measurements made by a spacecraft orbiting another planet have been accepted into the Minor Planet Center (MPC) database.
And while 3I/ATLAS poses no threat to Earth, the team say the exercise was a valuable contribution to planetary defence.
It showed that data on a comet captured from Earth could be combined with data on the same comet captured from a different planet.
And if future interstellar comets could be visited by a spacecraft, that would give scientists even more data to work with.
But the work isn't done yet. Scientists will get another chance at an observation of 3I/ATLAS from beyond Earth.
The Jupiter Icy Moons Explorer (Juice) is currently observing the comet just after its closest approach to the Sun, but the data won't be available until February 2026.
